Question

6. An organism is found to have an alternative enzyme step in glycolysis, shown below:

Fructose-1,6-bisphosphate -> two 1,3-bisphosphoglycerate

a. Write the corresponding reactions this would replace in glycolysis

b. Would glycolysis in this organism be more efficient?

c. Would other pathways or other parts of the cell be affected by this change?

Answer 1

Answer 6: An organism is found to have an alternative enzyme step in glycolysis, shown as above:

Fructose-1,6-bisphosphate -> two 1,3-bisphosphoglycerate

Answer 6a. The corresponding reaction this would replace in the glycolysis are as follows:

(1) Fructose 1,6-bisphosphate $\rightleftharpoons$ Glyceraldehyde 3- phosphate + Dihydroxyacetone phosphate

(Enzyme: Fructose bisphosphate aldolase)

(2) Dihydroxyacetone phosphate $\rightleftharpoons$ Glyceraldehyde 3-phosphate (Enzyme: Triosephosphate isomerase)

(3) 2 Glyceraldehyde 3-phosphate $\rightleftharpoons$ 1,3-bisphosphoglycerate

(Enzyme: Glyceraldehyde 3-phosphate dehydrogenase)

Answer 6b. No the glycolysis in this organism would not be more efficient since the efficiency of glycolysis depends upon the synthesis of ATP by substrate level phosphorylation and in both case 4 molecule of ATP is generated and among that two is consumed in preparatory phase. So the net molecule of ATP generated by both pathway i.e. glycolysis and its above given alternative pathway is 2.

But the above given alternative pathway bypass the glycolysis step i.e. step catalyzed by enzyme Glyceraldehyde 3-phosphate dehydrogenase at which step NADH is formed (which act as energy equivalent since it can generate 2.5 mole of ATP during oxidative phosphorylation in mitochondria). So since this step is bypassed in the above given alternative pathway so no molecule of NADH is formed. Thus there is loss of 2 molecule of NADH which will lead to overall loss of 5 mATP during oxidative posphorylation which will overall decrease the efficiency of cellullar respiration (thus also decreasing the efficiency of glycolysis).

Answer 6c. Yes the oxidative phosphorylation pathway will be affected by the above given alternative pathway of glycolysis due to bypass of the glycolysis step i.e. step catalyzed by enzyme Glyceraldehyde 3-phosphate dehydrogenase at which step NADH is formed (which act as energy equivalent since it can generate 2.5 mole of ATP during oxidative phosphorylation in mitochondria). So since this step is bypassed in the above given alternative pathway so no molecule of NADH is formed. Thus there is loss of 2 molecule of NADH which will lead to overall loss of 5 mATP during oxidative posphorylation.

This will also affect electron transport chain occurring inside the mitochondria since NADH is electron carrier which transfer the electron during electron transport chain from itself to other carrier such as cytochrome etc. So decrease in number of NADH will affect overall yield of electron transport chain.